9 month old daughter not sitting up unassisted and not crawling

My daughters will be 9 months at the end of September. She’s not really showing much interest in crawling. She sits up but not unassisted. She also uses a boppy pillow to help her sit up. I’m starting to worry. As she’s not a chubby baby. She is however rolling everywhere happily and quickly, she prefers to be on her back. I’m a first time mom so I don’t know if I should worry or not.

Can other more experienced moms share there experiences as well? I would really appreciate it!

Take care!